1. Field of the Invention
The present invention relates to devices for stopping rail mounted cars, carriages or the like at preselected positions and, in particular, to devices for controlling the movement of coke oven machinery whereby such machinery is accurately stopped at preselected locations within close tolerance limits.
2. Description of the Prior Art
The need to provide a means for accurately stopping rail mounted cars at certain preselected locations is one that is common to a number of industries. On coke ovens, for example, various types of rail mounted auxilliary equipment must be spotted then aligned with certain track side structures to carry out charging, pushing door removal and like functions. After such equipment has been initially spotted, it is often necessary to adjust its position relative to a charging hole, a coke oven door or some other track side structure. This alignment is often done visually by the operator, but recently various devices have been proposed to improve the accuracy, reliability or speed of this procedure. U.S. Pat. No. 4,196,471, for example, discloses a coke oven machinery, positioning and spotting system, in which system characteristics are mapped in a process memory and system dynamics are controlled by a central processing unit and a sensing mode. While this system provides highly accurate control of machine travel and positioning, it has been recognized that in some instances the use of a less complex and costly alignment device might be appropriate. Such a device is disclosed in U.S. Pat. No. 4,049,501. This device includes an alignment bar which is mounted at a selected position on a coke oven and a support rod which is mounted on a piece of coke oven machinery. Attached to the end of this support rod there is a coaxial tubular housing in which a feeler arm is mounted to pivot on its vertica1 axis. A portion of this feeler arm extends outwardly from inside the tubular housing and has at its terminal end a means for engaging the alignment bar. The device also includes electrical contactors positioned oppositely in the tubing and means for resiliently biasing the feeler with respect to the tubular housing. If the machine is properly spotted within a preselected spotting tolerance, the alignment bar will be directly aligned with the feeler arm so that the feeler arm will not pivot about its vertical axis. If, however, the machine has not been spotted with the desired degree of accuracy, the feeler arm will pivot so that a metallic probe attached to it will contact one of the electrical contactors. The probe and contactors are connected in electrical circuit with bidirectional means for moving the machine so that the machine is moved in the appropriate direction to effect alignment until the metallic probe comes out of contact wtih the electrical contactors, at which time alignment would ideally be achieved. It is found, however, that in using this device the speed of the machine will be relatively constant regardless of how far the machine needs to be moved to be correctly positioned. Thus, the machine may initially overshoot its intended stopping position and may then oscillate back and forth over this position before finally coming to rest. It is, therefore, the object of the present invention to provide a device for accurately stopping a piece of track mounted equipment at a particular position so as to avoid such oscillation about that position.